Following up on Michael's comment, I want to emphasize two more
implications of our proposed definition of baseline.
1. It may be possible for a user agent that doesn't support all of the
technologies listed in the baseline to render the content and operate
its functionality. However, the content only conforms to WCAG at the
specified level under the assumption that all of the technologies
included in the baseline are supported and enabled. Likewise, the
content may make use of technologies that are not in the baseline, but
again this doesn't affect conformance to WCAG (again at the specified
level).
2. We need to introduce "hooks" into the guidelines that make explicit
reference to the baseline. A draft of this has already been written, but
it has to be incorporated into the success criteria in all those places
where they rely implicitly on the baseline. In the past, this hasn't
been made plain in the document, in part because we didn't have a firm
strategy for dealing with these dependencies; but now that the concept
of baseline has solidified we need to make sure the success criteria
reflect it.